Various types of contaminants, including volatile organic compounds (“VOC”) and other adsorbable compounds may be contained in industrial fluid streams, such as air or water being exhausted from an industrial reactor, sewage treatment facility, distillation system or other chemical/industrial process equipment. In many instances, release of the adsorbable contaminants into the environment is prohibited or regulated due to the toxicity of the contaminants. In other instances, it may be desirable to recover and recycle the contaminants due to their high cost or scarcity.
A number of adsorption and desorption devices have been developed for enabling removal and/or recovery of adsorbable contaminants from contaminated fluid streams. These have included “fixed bed” adsorbers and desorbers wherein a fixed volume of an adsorbent material, for example, commercially available resin pellets, is contained. A feed stream, for example a gas having an adsorbable component, for example an adsorbable contaminant, is directed to enter one end of a packed bed of adsorbent particles, and the gas having at least some of the contaminant removed therefrom exits from another end of the bed. This process continues for a sufficient period of time, determined by the time when the adsorbent bed becomes saturated with the adsorbed components and the concentration of the contaminant gas in the exit stream begins to increase. Reducing the pressure and/or increasing the temperature of the adsorbent particles and by withdrawing the evolved contaminants from the adsorbent bed sometimes accomplish at this point regeneration of the adsorbent.
These fixed bed adsorption systems are highly inefficient from an operational standpoint. Fixed bed systems operate in a “batch mode” even when fluid flow into the adsorption system is continuous. This requires a plurality of fixed beds because each fixed bed is periodically taken off line for adsorbent regeneration and another fixed bed is brought on line to replace it. Fixed beds are designed for a specific flow rate and reasonable cycle time. This requires significant power usage under design conditions because of the high pressure drop. The fixed bed cannot operate efficiently when the contaminant stream flow rate is significantly lower than the design rate because of poor gas distribution causing lower overall contaminant capacity on the resin. A contaminant stream flow rate which higher than design flow rate causes higher pressure drops requiring larger blowers and thus higher operational costs.
In order to increase operational efficiency of the packed bed adsorption systems, a number of “fluidized bed” adsorbers have been developed, wherein adsorbent particles are placed within a series of perforated trays or containers within a unit, and a contaminated fluid stream is passed through the perforations in the trays or containers with sufficient velocity to cause movement or lifting of the adsorbent particles. The beds are designed to allow the resin to flow by gravity from the exit of one tray to the entrance to the next tray.
Fluidized beds in general allow for a reasonable adsorption of contaminant at a relatively high flow rate and low pressure drop. Continuously operating fluidized beds also allow for a variation in resin flow that is essential if the contaminant concentration changes. However, to get a high percentage of contaminant removal, more trays are required which increases pressure drop and resin inventory in the system. Fluidized beds must operate at a flow rate above the minimum flow rate for fluidization of the resin particles and below the minimum flow rate required for entrainment of the particles (carrying of the resin particles by the vapor stream). Fluidized beds also cause break up of the resin particles resulting in relatively high resin replacement.
The prior art has also included a flowing bed adsorption/desorption system wherein a flow of sorption media (i.e., an adsorbent) passes between narrowly spaced porous plates. A stream of contaminated air may flow inwardly through one porous plate, through the flowing bed of sorbent and outwardly through the other porous plate. Contaminants in the air are thus adsorbed by the sorbent. It is axiomatic, however, that the openings in the porous plates be smaller than the diameter of the sorbent particles to prevent the sorbent particles from escaping outwardly through the porous plates. This system is described in U.S. Pat. No. 6,562,113 B1 (Aykanian et al.), which is expressly incorporated herein by reference.
Other examples of adsorbers and desorbers of the prior art include but are not necessarily limited to those described in U.S. Pat. No. 5,628,819 (Mestemaker et al.), U.S. Pat. No. 5,149,342 (Mestemaker et al.) and U.S. Pat. No. 4,586,941 (Cooley), the entireties of which are expressly incorporated herein by reference.
In view of the shortcomings and limitations of the prior art, there exists a need for the development of new devices and methods for adsorption/desorption of adsorbable contaminants from fluid streams which allow for continuous exchange of the adsorbent without requiring interruption of the adsorption/desorption process and/or without the need for maintaining restricted range flow rates of the contaminated fluid stream or regeneration fluid stream in order to attain optimal performance of the system.
It is an object of the invention to provide an effective and efficient moving bed adsorber apparatus for removing contaminants from a fluid stream and/or replenishing spent adsorbent materials.
It is a further object of the invention to provide a moving bed adsorber apparatus that provides a means for optimizing adsorption by the adsorbent materials.
It is a further object of the invention to provide a moving bed adsorber apparatus that maintains a substantially constant depth or thickness of adsorbent free from bridging of the adsorbent particles.
It is a further object of the invention to provide a moving bed adsorber apparatus that can effectively process a fluid stream having a very low flow rate.
It is a further object of the invention to provide a moving bed adsorber apparatus that can effectively process a fluid stream having a very high flow rate
It is a further object of the invention to provide a moving bed adsorber apparatus that can process a high adsorbant mass flow using a relatively low adsorbent inventory.
It is a further object of the invention to provide a moving bed adsorber apparatus that causes relatively low mechanical abrasion of resin particles and thus has relatively low resin attrition.
It is a further object of the invention to provide a moving bed adsorber apparatus that can accommodate a wide range of operating conditions.
It is a further object of the invention to provide a moving bed adsorber that can be effectively operated using non-spherical adsorbent particles.
It is a further object of the invention to provide a highly effective, and highly efficient adsorption and desorption system to both remove adsorbable components from a fluid stream and recover the adsorbed components from spent adsorbent particles.
Other objects and aspects of the present invention will become apparent to those of skill in the art upon reading the following summary and detailed description.